Wireless communication systems are not new. Indeed, two-way radio technology dates back to the beginning of the 20th century, while its progeny, cellular telephony systems, were first introduced in the early 70's. As the technology developed and the cost associated with owning and using a cellular telephone decreased, the popularity of the wireless telephony systems exploded. To accommodate this growth in the subscriber base, digital cellular techniques were developed and standardized to increase user capacity of the cellular system without a commensurate increase in the radio frequency (RF) power generated within the system.
A number of different digital wireless communication technologies have been introduced and provide the basis for a number of wireless communication system architectures. Two primary examples of digital wireless technology are the time-division multiple access (TDMA) and code-division multiple access (CDMA) technologies. In a TDMA system, a carrier frequency is parsed into independent incremental units of time, referred to as a timeslot, wherein each timeslot at a carrier frequency supports an independent communication session between a subscriber unit (or, handset) and a communication station (or, base station). That is, while a communication channel in a conventional analog communication system is commonly defined by its carrier frequency (i.e., a frequency division multiple access (FDMA) system), a communication channel in a TDMA system is defined by a timeslot on a particular carrier frequency. Carving a given carrier frequency into N-independent timeslots results in an N-fold increase in system capacity over traditional FDMA system, with only a nominal increase in radiated power. In practice, an increase in capacity of two- to eight-fold has been achieved.
In a CDMA system, a communication channel is defined by a pseudo-noise (PN) code contained in the header of digital communication packets passed between the subscriber unit and the communication station. To further enhance system capacity, the CDMA system is a spread-spectrum system wherein the communication channel (defined by the PN code) hops through any of a number of carrier frequencies over an assigned band of radio frequency (or higher) spectrum.
While the introduction of such digital cellular techniques have certainly increased system capacity, developers of wireless communication system equipment continue to introduce enhancements designed to increase capacity and improve system performance. An example of such a development is the use of antenna arrays and, more particularly, the development and implementation of smart antenna technology. Antenna arrays introduce what is commonly referred to as spatial diversity, wherein each antenna in the array effectively provides a signal which is not correlated with the signals provided by other antenna in the array. These decorrelated (i.e., not fully correlated, as opposed to [completely] uncorrelated) signals provide the receiver with a number of alternative signals, each a decorrelated representation of the transmitted signal, from which the strongest is selected for downconversion and baseband recovery. On its own, diversity in the spatial domain provides multiple transmit and receive paths that serve to enhance both the uplink and downlink components of a wireless communication link. Smart antenna systems such as, for example, the IntelliCell® smart antenna technology offered by ArrayComm, Inc. of San Jose, Calif., provides further enhancements to the spatial diversity offered by an antenna array to further improve system performance characteristics. On the downlink side (from the communication station to the subscriber unit), spatial diversity facilitates improved directionality of the transmitted signal, which serves to extend the range of the downlink component without increasing power and reducing co-channel interference in the system. On the uplink side, the multiple antennas provide the receiver with a commensurate number of receive signals from which to choose.
Despite the introduction of spatial diversity, and the benefits to be gained from implementations of spatial diversity, many system operators still believe that their system coverage is constrained by the uplink component. While the improved directionality of the downlink component provided by smart antenna techniques may serve to increase the effective downlink range of the communication link, increasing the downlink component alone does not extend the effective range of the entire communication link. That is, it does not matter that the communication station is powerful enough to reach the subscriber unit if the uplink component cannot reach the communication station. Colloquially stated, the wireless communication channel is only as strong as its weakest link. If the communication channel is limited by its uplink component, increasing the strength of the downlink does not solve any problems.
Thus, a method and apparatus for extending the effective range of a communication link in a wireless communication system is required, unencumbered by the deficiencies and limitations commonly associated with the prior art. Just such a solution is presented, below.